DIV: ultrasonic camera

ABSTRACT

An ultrasonic camera having a high efficiency ultrasonic lens is coupled to a ultrasonic transmitter/receiver by a stretched membrane interface. The ultrasonic lens provides highly efficient transmission of ultrasound without introducing aberrations. The ultrasound system also uses a quasi incoherent source to reduce speckle noise in the image.

CROSS-REFERENCE TO CO-PENDING APPLICATION

This application is a divisional application of copending U.S.application Ser. No. 09/050,224, filed Mar. 28, 1998, which is acontinuation-in-part of U.S. application Ser. No. 08/621,112, filed Mar.22, 1996, now U.S. Pat. No. 5,732,706 issued Mar. 31, 1998.

FIELD OF THE INVENTION

The invention relates to an ultrasound camera imaging system and, moreparticularly, to an ultrasound imaging array with a high efficiency andaberration corrected ultrasonic lens, a quasi incoherent transmitter, alow volume fraction transducer based array and a stretched membraneinterface.

BACKGROUND OF THE INVENTION

Practical applications of ultrasonic imagers have suffered from poolultrasonic lenses. These lenses have poor ultrasound transfercharacteristics that attenuate the ultrasonic signal and introduceultrasonic aberrations. Additionally, ultrasonic imagers have used acoherent ultrasound source for insonification of the object. A coherentultrasound source does not provide a high quality ultrasound image. Theresulting image is “speckled”, in a manner somewhat similar to an imageobtained by a laser. Additionally, an ultrasonic imager requires amethod of effectively coupling an ultrasonic lens to an ultrasonicsensor with low signal loss.

Ultrasonic sensors are used in a wide range of applications,particularly medical imaging. Acoustic arrays configured as a twodimensional array of sensors using integrated circuit technology havebeen developed. Once such acoustic array, is disclosed in U.S. Pat. No.5,483,963 to Butler et al., issued Jan. 16, 1996, wherein certain rightshave been assigned to the assignee of the instant application. U.S. Pat.No. 5 483,963 is incorporated herein by reference. Butler et al.disclose a plurality of ultrasonic transducers arranged in a reticulatedtwo dimensional array, each sensor having a first independent electricalconnection, and each sensor having a second common electricalconnection. An integrated circuit signal processing means for processingsignals from the two dimensional array of ultrasonic transducers isconnected to each one of the plurality of ultrasonic transducers at thefirst independent electrical connection.

While known ultrasonic systems are useful, their operation is sometimesimpeded by cross talk interference transmitted from one ultrasonictransducer to another. Therefore, it is a motivation of the presentinvention to provide an improved ultrasonic image using a sensor thatreduces such deleterious effects from cross talk.

Further, transmitter elements in an ultrasonic system require relativelyhigh voltage. Therefore, known ultrasonic arrays comprise circuitrycapable of operating under high voltage conditions. The use of suchrelatively high voltage precludes constructing electronic integratedcircuits to operate both receiver and transmitter elements with lowvoltage CMOS integrated circuit technology. CMOS has inherent advantagesof relatively small size and low power. Therefore, it is anothermotivation of the present invention to provide an ultrasonic systemcomprising a low voltage receiver array electronics having high voltagetransmitter circuitry in the same integrated circuits.

Ultrasonic systems use an ultrasonic transducer to convert electricalenergy into sound energy. The sound energy produced is directed at anobject, such as biological tissue, or objects immersed in water. Objectsin the ultrasonic wave path reflect ultrasonic signals back to theultrasonic transducer with varying degrees of efficiency. The transducerdetects sound that is reflected back to the transducer and providessignals that may be processed to produce an image of the object.

Ultrasonic transducers are provided in linear transducers or rectangulartransducers, wraith an array of ultrasonic detectors and transmitters. Alens system is incorporated in the system to focus the ultrasonic signalon the detector.

The performance of ultrasonic transducer systems may be improved byincreasing the amount of ultrasonic energy available to the ultrasonicdetector. This may be accomplished with a more efficient lens system.

Ultrasonic lens systems suffer from aberrations caused by astigmatism,coma, spherical aberration and distortion. These aberrations reduce theability of the ultrasonic imager to resolve fine detail and may renderthe imager unsuitable for a given application.

Accordingly, there is a need for an ultrasonic imager having a highefficiency lens incorporating an efficient sensor/lens interface with aquasi incoherent transmitter utilizing a low volume fraction transducer.

SUMMARY OF THE INVENTION

The invention provides an ultrasonic camera comprising a camera housingand a means for collecting ultrasonic energy at high efficiency withhigh accuracy connected to the camera housing. The camera further has ameans for transducing the collected energy into electrical signals, anda means for processing the electrical signals into an image.

The invention further provides an apparatus for generating, quasiincoherent ultrasonic insonification with a first group of coherenttransmitters. The apparatus for generating quasi incoherent ultrasonicinsonification also includes a second group of coherent transmitterswhere the first group transmits a different ultrasonic signal from thesecond group.

The invention further provides an acoustic interface having a mount witha flat surface surrounding an opening through the mount. A membrane isstretched over the flat surface. A means for retaining the membrane isattached to the mount and the membrane is held taut to the mount by theretaining means.

The invention further provides an ultrasonic lens system comprising alens housing having a mount and a plurality of ultrasonic elementsattached to the mount wherein the plurality of ultrasonic elementscooperate to transmit ultrasonic radiation at high efficiency with lowaberration.

The invention further provides an ultrasonic lens system having a firstultrasonic lens made from polystyrene having a first radius of curvatureof about −79.35737 mm, and a second radius of curvature of about−162.88524 mm, with an aspherical surface defined by the equation:$\begin{matrix}{Z = {\frac{{cx}^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {Ax}^{4} + {Bx}^{6} + {Cx}^{8} + {Dx}^{10}}} & (1)\end{matrix}$

where c=1/radius, radius=54.76050 mm, K is the conic constant which iszero 0.0 in this case, A=−0.433031E-05, B=0.594032E-9, C=0.157306E-12,and D=−125397E-15, and a first thickness through the ultrasonic centerof 3.72 mm; and a second fluid filled ultrasonic lens made frompolystyrene having a third radius of curvature of about 54.76050 mmwithin a second aspherical surface defined by the equation:$Z = {\frac{{cx}^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {Ax}^{4} + {Bx}^{6} + {Cx}^{8} + {Dx}^{10}}$

where c=1/radius, radius=89.89027 mm, K is the conic constant which iszero 0.0 in this case, A=−0.679678E-06, B=0.463364E-11, C=0.146454E-13,and D=−0.179238E-17, a third aspherical surface with a fourth radius ofcurvature of 89.89027 mm having a fourth aspherical surface defined bythe equation:$Z = {\frac{{cx}^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {Ax}^{4} + {Bx}^{6} + {Cx}^{8} + {Dx}^{10}}$

where c=1/radius, radius=89.89027 mm, K is the conic constant which iszero 0.0 in this case, A=−0.679678E-06, B=0.473364E-11, C=0.146454E-13,and D=0.179238E-17, and a second thickness through the ultrasonic centerof 7.44 mm, a fifth radius of curvature of about −578.81495 mm locatedabout 89.028 mm from the fourth radius, and a sixth radius of curvatureof about −578.81495 mm with a third thickness through the ultrasoniccenter of 2.48 mm.

Other objects, features and advantages of the present invention willbecome apparent to those skilled in the art through the description ofthe preferred embodiment, claims and drawings herein wherein likenumerals refer to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate this invention, a preferred embodiment will be describedherein with reference to the accompanying drawings.

FIG. 1 shows an isometric drawing of a portion of an ultrasonic arrayand an integrated circuit made in accordance with one aspect of thepresent invention.

FIG. 2A and FIG. 2B schematically illustrate a top view and a side view,respectively, of a pattern of a receiver array.

FIG. 3A and FIG. 3B schematically illustrate a top view and a side view,respectively, of a pattern of a transducer array comprising transmit andreceive elements made in accordance with one aspect of the presentinvention.

FIG. 4, FIG. 5 and FIG. 6 schematically illustrate patterns of furtherexamples of transducer arrays comprising transmit and receive elementsmade in accordance with alternate embodiments of the present invention.

FIG. 7, FIG. 8 and FIG. 9 schematically show example patterns oftransducer arrays comprising transmit and receive elements using a highvoltage circuit path to connect selected transmitter elements.

FIG. 10 illustrates cross talk properties in an ultrasonic array.

FIG. 11 schematically illustrates a cut away side view of an alternateembodiment of the bump bonding features of the invention.

FIG. 12 illustrates a further alternate embodiment of a matching layer.

FIG. 13 schematically shows an example of an ultrasonic lens.

FIG. 14 schematically shows an example of a matching layer created inthe surface of the lens.

FIG. 15 schematically shows a cut away view of a partial ultrasonicarray made in accordance with one aspect of the present invention.

FIG. 16 shows a schematic of an ultrasonic array and system of theinvention imaging a target.

FIG. 17 shows an example of target imaging optimization in accordancewith one aspect of the invention.

FIG. 18 shows phasing time information of typical piezels illustrated inFIG. 17.

FIG. 19 illustrates transmit piezels having spatially associated receiveand/or transmit piezels.

FIG. 20 schematically illustrates an overview of an ultrasonic system ofthe present invention employing a multi-element acoustic lens.

FIG. 21 schematically illustrates one embodiment of on-chip electroniccircuitry incorporating an analog-to-digital converter constructed on anintegrated circuit employed in one aspect of the invention.

FIG. 22 shows the ultrasonic imaging system of the invention.

FIG. 23 shows the ultrasonic lens of the ultrasonic imaging system ofFIG. 22.

FIG. 24 shows an alternate lens of the ultrasonic imaging system of FIG.22.

FIG. 25 shows a stretched membrane interface used in the ultrasonicimaging system of FIG. 22.

FIG. 26 shows an ultrasonic transmitter used in the ultrasonic imaginesystem of FIG. 22.

FIG. 27 shows an ultrasonic imaging system with an alternate ultrasonictransmitter system.

FIG. 28 shows an acoustical transducer hybrid array having an array oftransducer elements.

FIG. 29 plots the piezoelectric coupling co-efficient, capacitance andsensitivity at a constant resonance frequency as a function ofpiezoceramic volume fraction.

FIG. 30 shows an ultrasonic lens system for transmitting ultrasonicradiation at high efficiency with low aberration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Refer now to FIG. 1, FIG. 1 shows a schematic isometric drawing of aportion of an ultrasonic array and an integrated circuit made inaccordance with one aspect of the present invention. The ultrasonicarray comprises a plurality of piezoelectric transducer elements, or“piezels”, 41, 43, 45, 47 and 49. The piezoelectric transducer elementsinclude interspersed transmitter elements T (such as elements 41 and 43)and receiver elements R (such as elements 45, 47 and 49). Eachtransducer element, or piezel, 41, 43, 45, 47 and 49 comprisesultrasonic transduction material, such as a suitable compositepiezoelectric material known in the art. Indium bumps 52 and 53 bondeach receiver element R to an integrated circuit, such as CMOS VLSIintegrated circuit 55. Insulation material 54 insulates each transmitterelement T from the CMOS VLSI integrated circuit 55. Selected rows orgroupings of transmitter elements may advantageously be connected by,for example, high voltage conductor paths 57 wherein the high voltageconductor paths 57 are laid over the insulation material 54 insulatingthe high voltage conductor paths 57 from semiconductor substrate 50. Inthe case of a traditional CMOS VLSI circuit, the insulation material 54may be the same as the circuit passivation layer. Alternatively aninsulated metal line within the circuit may, or may not, in turn, becovered with an insulator. It will be understood that a plurality ofsuch high voltage conductor paths 57 may be similarly constructed forconnecting transmitter elements throughout an array of elements. Highvoltage conductor path 57 may advantageously be connected to othersimilar high voltage conductor paths and to external transmissioncircuitry (not shown) of conventional design. As a matter of designchoice, the high voltage conductor paths may be joined together orseparately connected to the external transmission circuitry to enablephasing of transmit elements.

Acoustic array 12 optionally comprises a protective seal and cover withan outer matching layer 44, one or more matching layers 147 and a commonelectrically conductive electrode 46. By matching the acoustic impedanceof the piezoelectric detector 48 with that of body tissue through theuse of matching layers 44 and 147, transducer sensitivity increasessharply. The outer matching layer 44 may comprise an acoustic materialor composite material having an acoustic impedance suitable for couplingof energy to the transducer elements. Plastic or tungsten-loadedaraldite has been used to make quarter wave matching layers. SeeDiagnostic Ultrasonics: Principles and Use of Instruments by W. M.McDicken (1999). The common electrode 46 may comprise a thinner layer ofa conductor, such as gold or nickel, for example, for contact to thepiezoelectric layer 48.

The individual receiver piezels 45, 47 and 49 may be advantageouslyhybridized onto the silicon read out IC (ROIC) 55. A saw cutreticulation has been made completely through the ceramic PZT layer 48up to the common electrode 46. By cutting all the way through the PZTlayer 48, electrical and mechanical cross talk can be reduced, therebyimproving the resolution of the directed beam, as sell as thesensitivity to the received signal. Cutting of the transducer material48 through to the common electrode 46 increases inter-element isolation.Furthermore, by using air in between the piezels 41, 43, 45, 47 and 49as an acoustical insulator, acoustic cross talk can be reducedsignificantly as well. Air isolation between elements, or a fillermaterial such as epoxy, silicone, plastic or other equivalent materialsembedded between elements can significantly reduce cross talk in bothdirections thus improving system resolution.

It is well known that sub-reticulation within an element may be alsoused to create a composite detector. The special structure of the deviceof the invention is particularly well suited for fabrication of twodimensional arrays because the tops of the transducers are connected bythe common electrode 46 and matching layers and the other side isconnected via the bump bond to the multiplexer.

Additional available space on the active surface of the semiconductorallows the integration of other active electronic circuitry, such aspre-amps, sample holds, peak detectors and an on-chip analog-to-digitalconverter. The integrated analog-to-digital converter as illustrated inFIG. 21 would have the following advantages: reduced power, improvedtransmission of signals over the cables, and reduced conversion rates byperforming analog to digital conversion before multiplexing rather thanafter signal multiplexing.

FIG. 2A and FIG. 2B schematically illustrate a top view and a side view,respectively, of a pattern of a receiver array, wherein each of thetransducers in the array function to receive signals. In one example ofsuch a configuration, a separate array of transmitters (not shown) maybe employed to transmit signals. In another example of such aconfiguration, receiver and transmitter functions may be switched usingthe same elements, but applying different control signals, as discussedhereinbelow with reference to FIG. 15. In the aforementioned switchedconfiguration, relatively higher voltage DMOS circuitry, instead of CMOScircuitry, may be employed to carry out the functions of ROIC 55.Ultrasound imagery, as traditionally constructed, requires transmissionof a single pulse and then “listening” to returning echoes. An image isthen constructed from the varying time-dependent intensity of thereturned signal. The array permits the sampling and storage for eachelement directly behind each element. The amount of signal processingand sample storage in the ROIC is limited only by conventional circuitdesign rules.

FIG. 3A and FIG. 3B schematically show an array 116 of receivers 114 andtwo linear arrays of transmitters 112. FIG. 3A shows a top view of thearrays 116 and FIG. 3B shows a side view of the array 116. FIG. 7 showspower routing for the transmitter arrays of FIGS. 3A and 3B. Highvoltage and control line 16 is connected to each transmitter 112 in thelinear array 116. Similarly, high voltage and control line 154 connectseach transmitter in linear array 111. Independent high voltage andcontrol lines 154 and 156 provide independent switching of lineararrays. The multiple transmit elements may advantageously be wired to bepulsed simultaneously or pulsed in groups permitting transmitbeamforming as in conventional ultrasound. Use of the high voltage andcontrol lines 154, 156 enables the transmission of relatively highvoltage signals to the transmission elements from an externaltransmission circuit, wherein the external transmission circuit may beof a conventional design. Thus, since the transmission circuitry may beimplemented externally, the ROIC comprises relatively lower voltageCMOS, allowing for very dense circuitry. Thus, the apparatus of theinvention allows increased signal processing and/or time sampling totake place in the ROIC. As a result, significant parallel signalprocessing may be implemented using CMOS circuitry in accordance withknown practices.

FIG. 4 schematically shows an array 118 of receivers 119 and four lineararrays of transmitters 120, 122, 124 and 126. Transmitters 120, 122, 124and 126 are positioned in a diagonal configuration. FIG. 8 shows powerrouting for the transmitter arrays of FIG. 4. High power line 158 isconnected to each transmitter in linear array 120. Similarly, high powerline 160 connects each transmitter in linear array 122. High power line162 connects each transmitter in linear array 124 and high power line164 connects each transmitter in linear array 126. As in theconfiguration of FIG. 7, independent high power lines provideindependent switching of linear arrays 154 and 156.

FIG. 5 schematically shows an array 128 of receivers 134 andtransmitters 132. The transmitters 132 are configured in generallycircular arrangements 130, 132. FIG. 9 shows a generally circulararrangement of transmitters 132 among receivers 134. High voltage andcontrol line 166 is connected to each transmitter, in generally circulararrangement of transmitters 132. Outer circular arrangements oftransmitters are provided with separate switching lines to provideindependent activation of each set of transmitters.

FIG. 6 schematically shows an array 138 of receivers 148 and apredetermined pattern of transmitters 140, 142, 144 and 146. Independenthigh voltage and control lines may be connected to each transmitterindependently or each transmitter may be connected by a single highpower supply line.

As discussed above with respect to, for example, FIG. 3A, in oneembodiment of the invention, the arrays are built with low voltage CMOS.Use of CMOS, as compared to other circuit technologies, allowsminiaturization that permits dynamic electronic focus in both directionsusing cell based logic and circuitry. A form of such dynamic electronicfocusing is known in the field of phased array radar, but was previouslylimited in ultrasound to steering the beam in one direction only; suchas in transmit only, receive only, or both. The two dimensional arraywith active circuitry directly behind each element makes possiblefocusing or steering the beam in both directions. The result of suchfocusing and steering is a sharper picture and/or increased flexibility.

FIG. 10 illustrates the effect of signal cross talk. Signal cross talkis generated by the operation of one piezel affecting other elements ofthe array. Element 168, connected by indium bump bond 174 to bump bond176 connects to active device layer 194. Active layer 194 is depositedon semiconductor substrate 196. Ultrasonic element 168 receives ortransmits signal 186. Signal 186 is shown as a wave train thatpropagates to the other array elements such as transducer elements 170and 172. Active layer 194 and substrate 196 act to transmit waves orportions of waves 188 of the signal 186 though indium bump bonds 180 and178 to element 170. Cross talk generates wave train 190 in piezel 170.Active layer 196 and substrate 194 act to transmit waves 188 of signal186 though indium bump bonds 184 and 182 to element 172. Cross talkgenerates wave train 192 in piezel 172.

The size of the bump interconnections 182 and 184, 178 and 180, 174 and176 is particularly significant in controlling the acoustic propertiesof the back surface of the transducer 168, 170 and 172 and thus also thecross talk resulting from acoustic energy received or transmitted by oneelement that subsequently influences another neighboring element.Ideally, transducer elements would be completely isolated. If such werethe case, then energy impinging on, or transmitted by, one element wouldhave no effect on its neighbors and each element would be independent.Air is an excellent isolator for ultrasound but, without the structureof the present invention, there has not been a means to approach theideal case. Prior to the present invention, problems associated withreducing cross talk were in the physical implementation of thetransducer array structure. In order to sense the electrical energy inthe transducer. there must be either a hard electrical connection or anextremely efficient and precisely impedance-matched capacitive couplingestablished. Historically, structures employed have been constrained forfabrication purposes to being held together with appropriate attenuatingor reflecting adhesives and glues to absorbing conductive substrates. Incontrast to previously known structures, the new structure of thepresent invention approximates the ideal case. The top surface isconnected only by the common electrode 503 which is incorporated intothe matching layer 501. The bottom of the transducer 192 is contactedonly by bump 182. The sides are isolated by air or other material asdiscussed above to improve mechanical stability. If the bump 182 ismaintained at a size which is small with respect to the element endarea, cross talk transmitted by the bump becomes insignificant and canbe ignored. Maintaining a bump size less than about 10-20% of the sizeof the piezel contact area appears from electrical models to be thecritical point where the size effect is most significant. This is adirect function of bump area with respect to element area.

The primary effects from any mechanical connection which are undesirableare: (a) conduction of the ultrasound energy into the mounting surfacewhere it would be re-radiated and detected by neighboring elements; and(b) constraint of the transducer material by the contact which wouldprevent the full piezoelectric response. Of these two effects, the firstis the larger and more deleterious, but both are reduced by smallcontacts. If the bump required the full area, then the amount of energytransferred into the substrate would only be a function of the acousticproperties of the bump material with respect to the transducer materialand the substrate. For the simplified case of no attenuation by thebump, all energy falling on each element should be re-radiate to itsneighbors with only the attenuating properties of the substrate tocontrol re-radiation. However, if the bump is small, it will act as anattenuator because only the area fraction occupied by the bump willconduct the energy. Thus, with a 10% area fraction, only 10% of theenergy will be conducted into the substrate. To be sensed by a neighbor,the energy must pass through a second 10% attenuator and thus reduced byanother factor of ten. The result would be 1% cross talk, 99%attenuation, if the bump and substrate had no attenuating properties. Ifthe bump area were reduced to 5%, a 0.25% cross talk, 99.75%attenuation, would result.

This effect is independent of the substrate, and so would be equallyapplicable for traditional transducers and substrates including, but notlimited to, read out integrated circuits. This effect permits electricalcontact to the isolated side of a transducer without adding asignificantly acoustically conductive path.

FIG. 11 shows one alternate aspect of the invention to reduce signalcross talk. Small indium bumps 200, 202 and 204 connect transducerelements 1194, 1196 and 1198 to stepped bond connectors 206, 208 and210, respectively. Stepped bond connectors 206, 208 and 210 and bumps200, 202 and 204 are surrounded by an electrically insulating materialsuch as air, one of many known epoxies or silicone based materials.Filler material, if desired, can be injected into the gap around thebump bonds to provide stabilization. Selection of the filler materialmay be based upon acoustical and electrical impedance to minimize crosstalk. The graded structure of the stepped bond connectors permits thetailoring of the acoustic properties of the interconnection layer 212between the piezoelectric elements and the mounting substrate 214. Byadjusting the area and volume fractions of the electrical connections,the acoustic properties of the interconnection layer can be adjusted.

FIG. 12 shows a cross section of a stepped matching layer for array 230.Common electrode 224 is connected to matching layer 1226, which on oneside is flat and on the other is configured in a step arrangement.Matching layer 2228 has a matching step arrangement. Transducers 218,220 and 222 are connected in the fashion of FIG. 1 to common electrode224. The stepped matching layers act to dampen cross talk signalsgenerated by transducers 218, 220 and 222. The step sizes in matchinglayers 226 and 228 are selected to be small with respect to thewavelengths of the ultrasound.

FIG. 13 shows a concave lens of the invention and FIG. 14 shows aserrated concave lens of the invention. The prior art is constrained toselect materials which have the desired acoustic properties as intrinsicproperties. As contemplated by the present invention, desired materialproperties may be constructed from two different materials. Surfacefinish geometries of lateral area and thickness may advantageously beselected to be significantly less than a wavelength in order to reducediffraction effects. In the simplest case, if graded material propertieswere to be constructed, binary optic structures might be used to make agraded interface, where one side of the interface fully comprised afirst material, the other side comprised an entirely different materialand the intervening layers comprised different area fractions of the twomaterials. This could be expanded to have multiple materials in thestack to yield multiple variable properties. Or, if there bias nomaterial with the correct initial properties, such a graded or slopedstructure could be constructed from two different materials applied inthe proper area percentage to obtain a desired average properties.

Some experimental evidence in support of this approach is available.Lenses were fabricated by Lockheed Martin IR Imaging Systems. Inc. ofLexington, Mass. USA. The lenses are relatively rough but, because theroughness is less than wavelength dimensions, there is little or noeffect, as evidenced by an excellent, nearly theoretical performance ofthe lens. In another example of a matching layer, a lens having aninherent surface roughness may be used in the above type of structure inthe lens surface. The surface may advantageously be immersed in fluidthat fills any open space between the lens and the transducer array,thereby creating an inherently graded matching, anti-reflection surfacewithout a coating. Creating such a graded lens surface may be done usingany suitable known process such as, for example, machining, molding, orany method of material deposition. The possibility of molding in ridgesis particularly attractive since it would require no additional steps tocreate a graded matching surface. Furthermore, the approach, because itincorporates the fluid surrounding the lens, is inherently selfcorrecting if the fluid properties change significantly.

FIG. 15 shows an alternate embodiment of the invention including an anyof transducers 300. Cross talk is reduced in the configuration of FIG.15 by isolating upper and lower matching layers by cutting in betweenthe matching layers for each transducer. Common electrode 318 serves toconnect one side of the transducer array. Transducers 320, 322, 324 and326 may advantageously be indium bump bonded to active layer 344. It isbelieved that full reticulation of the upper and lower matching layers,up to the common electrode 318, results in better signal coupling andbetter isolation between elements.

FIG. 16 shores a schematic of the array 412 of the invention imaging atarget 428. Piezoelectric array 412 comprises a plurality of piezelsrepresented by piezels 414, 416 and 418. Alternately, FIG. 16 couldfunction in a bistatic mode with separate transmit and receivetransducers but with similar microprocessor or PC monitoring, controland selection of any suitable combination of transmit elements andreceive elements. High voltage switch 410 switches the signal from thearray to either the receive electronics 408 or the transmit electronics406. The receive electronics 408 interface to a microprocessor orpersonal computer 402 having a memory 404 in a conventional manner. Thetransmit electronics also interface to the microprocessor or personalcomputer 402 in a conventional manner. The microprocessor 402 stores theidentity of those piezels that provide a usable signal from the target428. The array may be scanned in a regular fashion or in a randomfashion to determine which piezels should be used. In one embodiment ofthe invention, clusters of piezels may be used to boost signal strength.For example, groups of piezels of predetermined number, such as 4, 9 or16 piezels, are triggered to send out a pulse. The signal returned fromthe target is evaluated for clarity. If the signal is useable from aparticular piezel the identity of the piezels is stored in memory 404.If the signal returned from the target is unusable, or has a relativelylow signal to noise value, the piezel is deleted from this array/targetcombination because probably both transmit and receive capability iscompromised simultaneously.

For example, during an echo cardiogram using a large array that may bean inch or two along one axis, some of the elements would be blocked byrib bones 476. 430. The signal from the blocked piezels would not beused to receive or transmit. In this example, since each element is atransmitter or receiver, the array could be constructed from DMOS. Inone alternate embodiment of the invention, some piezels may be phaseddifferently to improve sensing of the target. The computer would selectspatial location of the piezels used to sense the target and canadditionally temporally adjust the send/receive waves so that they areoptimized for best clarity.

In one embodiment, the high voltage switch is comprised of a DMOS, ordouble diffused metal oxide semiconductor, transistor. In an alternateembodiment, one or more of the high voltage switches may be electricallyactuated to connect the complementary ultrasonic transducer to thecamera's electrical ground. In another embodiment, the activation of thehigh voltage switches is controlled by a microcontroller, microprocessoror other semiconductor device. In another embodiment, the pattern ofactivation of the high voltage switches creates one or more groups oftransmitters from the plurality of transmitters. In another embodiment,one or more groups of transmitters selected by the high voltage switchesare driven sequentially through the common electrode to produce separateimages of the object. In another embodiment, the signal processorconnects these sequential images to produce a high quality image. Inanother embodiment, a DC voltage is applied to the common electrode anda pattern of high voltage switches are connected to an electrical aroundby a short activation pulse or a series of activation pulses to createan ultrasonic transmitter pulse, in another embodiment, the commonelectrode is connected to an electrical ground and a pattern of highvoltage switches are connected to a DC voltage on the substrate by ashort activation pulse or a series of activation pulses to create anultrasonic transmitter pulse.

Now referring to FIG. 17 where an example of target imaging optimizationis shown. A first piezel 502 transmits a pulse 504. A second piezel 506,spatially separated from the first piezel 502, transmits a pulse 508. Asshown in FIG. 18, first piezel 502 may best highlight target tissue 510at time 512 and second piezel 506 may best highlight target tissue 510at time 514. The computer 402 stores the preferred phasing timeinformation of each piezel 502, 506 so that a composite picture fromeach piezel 502, 506 is made from the best temporal data. The computeroptimizes an image by selecting piezels spatially, and associating apreferred phasing for each selected piezel.

In one embodiment, the first piezel 502 and the second piezel 506 mayeach comprise a transmit and receive piezel. In an alternativeembodiment, as shown in FIG. 19, each transmit piezel 516, 520 may havea spatially associated receive piezel 518, 522. For example, acheckerboard pattern of transmit piezels and receive piezels wouldprovide for spatially associated transmit and receive elements. In bothembodiments, the computer 402 stores the preferred phasing time betweentransmission and reception to provide for optimal phasing.

Now referring to FIG. 20, an overview of an ultrasonic system of thepresent invention employing a multi-element acoustic lens isschematically illustrated. The ultrasonic system 2000 includes a housing2001, an ultrasonic window 2003, a multi-element lens 2005,piezoelectric material 2030, silicon integrated circuit 2040 andoptional transmit transducers 2006.

In operation, the ultrasonic window 2003 may be in contact with, forexample, body tissue 2010. The multi-element acoustic lens may compriseat least two lenses 2002, 2004 where lenses 2002, 2004 may beconstructed as discussed hereinabove with reference to FIG. 14, forexample. Piezoelectric material 2030 may be constructed as one of theultrasonic arrays as described herein. Optional transmit transducers2006 may be of conventional design or be constructed in accordance withan embodiment of the apparatus of the present invention as describedhereinabove. The housing 2001 may advantageously be filled with a knownultrasound coupling fluid 2020 or equivalent. Piezoelectric material2030 and Silicon integrated circuit 2040 are electrically connected asdescribed herein with, for example, bump bonding techniques.

FIG. 21 schematically illustrates one embodiment of an analog-to-digitalconverter constructed on an integrated circuit 2100 employed in oneaspect of the invention. The integrated circuit 2100 comprises aplurality of similarly constructed unit cells 2112, an analog-to-digitalconverter (ADC) 2120, a buffer 2122 and a multiplexer 2124. In oneuseful embodiment, 64 such unit cells may be constructed on a silicondie of about 12 mm by 10 mm.

Each unit cell 2112 may comprise a bump 2104 for connection to anultrasonic transducer array, a sample-and-hold circuit 2110, a shiftregister 2108, a variable gain preamplifier 2102 and an output 2106. Theelements are connected and operate according to conventional integratedcircuit design rules. Each unit cell output 2106 is coupled to anon-clip ADC for converting analog, signals representing ultrasonicenergy to digital signals for further processing. In one usefulembodiment, the on-chip ADC 2120 may comprise a 10 bit, 5microsecond/sample ADC. The ADC 2120 is coupled to a buffer such as, forexample, a first-in-first-out (FIFO) buffer 2122. Buffer 2122 is coupledto a multiplexer 2124 that provides an output 2126 to externalprocessing circuitry. In one example embodiment of the invention, themultiplexer output may be a 10 bit parallel output.

Refer now to FIG. 22 which shows one embodiment of the ultrasonic system2310 of the invention. An object 2304 positioned at an object plane isinsonified by an ultrasonic transmitter 2316. The transmitter transmitsquasi incoherent ultrasound and is shown in more detail in FIG. 26. Inone embodiment, the ultrasonic transmitter 2316 transmits ultrasonicenergy with a wavelength of about 300 microns. Those skilled in the artwill recognize that ultrasonic energy having various other wavelengthsmay be used without deviating from the spirit and scope of theinvention. The object 2304 reflects the ultrasonic energy with varyingdegrees of effectiveness. Part of the reflected energy will fall on theultrasonic lens system 2314. The ultrasonic lens 2314, positioned onultrasonic axis 2302, receives the energy reflected from the object 2304and transmits it to the ultrasonic array 2312.

The ultrasonic lens 2310 is constructed from a body 2320 and a lenssystem 324 that is shown in more detail in FIG. 23. The ultrasonic lensmay be constructed using conventional lens making methods, includingmilling on a lathe, molding, injection molding, and other approaches tomachining and chemical processing. The ultrasonic lens 2314 focuses theultrasonic signal on the ultrasonic array 2312. The ultrasonic array ismounted behind a stretched membrane interface 2318. The stretchedmembrane interface 2318 is shown in more detail in FIG. 25. Theultrasonic array 2312 provides a two dimensional image of the object2304 on image output line 2328. The two dimensional image is thenprocessed with ultrasonic signal processing techniques described above.

In operation, the transmitter 2316, driven by a power amplifier 2330,sends a short pulse of ultrasonic energy into the fluid medium 2332 inthe direction of arrow 2325. In one example, the fluid medium 2332 iswater. The ultrasonic energy is then reflected off a target, such asobject 2304, in the object plane of the ultrasonic lens system 2324,also known as an acoustical lens system 2324. The acoustical lens system2324 focuses an image of the object 2304 onto the ultrasonic receiverarray, also known as an acoustical focal plane array or a transducerhybrid assembly THA. The THA has a readout through additionalelectronics controller 2334 and a real time display is presented to theuser on display device 2338. In one preferred embodiment, the acousticalfocal plane array may be constructed following the methods describedherein.

The ultrasonic camera 2310 housing 2340 encloses an ultrasonic medium2344, such as water or other suitable ultrasonic transmission medium. Afluid tight lens housing 2342 contains similar ultrasonic medium 2345and 2346. The fluid tight housing 2342 is attached to a mounting flange2341 on a stretch membrane mount 2402.

Refer now to FIG. 23 and FIG. 30 which show the ultrasonic lens systemof the invention. The ultrasonic lens system 2230 is designed to operatewith fewer elements and to efficiently transmit ultrasonic energy. Theultrasonic lens system 2210 comprises a housing 2212 that houses threeultrasonic elements, a ultrasonic lens window 2214, a polystyrene lens2216 and a fluid filled polystyrene lens 2218. The fluid filled lens2218 is shown as two lens 221 and 2219, in FIG. 30, held by housing 2212with fluid 2228 between. An ultrasonic window 2214 is mounted to thehousing 2212. Within the housing is an ultrasonic conductive materialsuch as water 2226.

The window 2214 is slightly curved with a first surface S1 radius ofabout 646.56671 mm and a second surface S2 radius of about 830.829136mm. The window is constructed from TPX, otherwise known aspolymethylpentene. The window is provided for medical imagingapplications to provide a standoff for the lens. The fluid materialbetween the window and the first ultrasonic element creates the start ofthe ultrasonic path from the object. In the case of underwater, or underpetroleum, applications, the window is not needed.

The next ultrasonic element in the lens system is a polystyrene lens2216 that is located behind the window 2214. The polystyrene lens 2216is 76.728 millimeters in diameter and is of an aspherical shape. Thefirst surface S3 of the polystyrene lens 2216 has a radius of about−79.35737 mm. The second surface S4 of the polystyrene lens 2216 has aradius of about −162.88524 mm and an aspherical shape defined by thefollowing equation:$Z = {\frac{{cx}^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {Ax}^{4} + {Bx}^{6} + {Cx}^{8} + {Dx}^{10}}$

Where c=1/radius, radius=−162.88524 mm, K is the conic constant which iszero 0.0 in this case. A=−0.19759E-05, B=0.157598E-10, C=−0.201574E-12,and D=0.0. The equation defines a curve that is revolved around theultrasonic axis 2225 to construct the ultrasonic lens shape.

The next ultrasonic element is a circular stop 2232 having an insidediameter of 63.657 mm and an outside diameter of 89.739 mm. The circularstop 2232 is positioned 89.028 mm from the polystyrene lens 2216.

The next ultrasonic element is a fluid filled compound lens 18 made of afluid cavity 2228 in a polystyrene body 2218. The first aspheric surfaceS5 of the fluid filled compound lens 18 has a radius of about 54.76050mm and an aspherical shape defined by equation 1. For this element,c=1/radius, radius=54.76050 mm, K is the conic constant which is zero0.0 in this case, A=−0.433031E-05, B=−0.594032E-9, C=0.157306E-12, andD=−125397E-15. The equation defines a curve that is revolved around theultrasonic axis 2225 to construct the lens shape. The second asphericsurface S6 of the polystyrene lens 2216 has a radius of about −89.89027mm and an aspherical shape also defined by equation 1. For this element,c=1/radius, radius=89.89027 mm, K is the conic constant which is zero0.0 in this case, A=−0.679678E-06, B=0.463364E-11, C=0.146454E-13, andD=−0.179238E-17. The equation defines a curve that is also revolvedaround the ultrasonic axis 2225 to construct the lens shape. The fluidcavity is formed by a third surface S3 with a radius of about −578.81495mm and a fourth surface S4 also with a radius of about −578.81495 mm.The fluid cavity is filled with FC40, a fluorocarbon fluid in which thevelocity of sound is less than water and having a high density. Otherfluids with a similar index of refraction may also be used.

The ultrasonic receiver transducer is shown at the focal point of thelens system 2210.

Refer now to FIG. 30 which shows an ultrasonic lens system 2230 maycomprises a lens housing 2212 having a mount, and a plurality ofultrasonic elements 2216, 2218, 2219, attached to the mount, wherein theplurality of ultrasonic elements cooperate to transmit ultrasonicradiation at high efficiency with low aberration. High efficiency isachieved by surface treatments 3000, 3002, 3004 that adjust the acousticimpedance of the solid to the surrounding fluid. The surface treatments3000, 3002, 3004 may comprise a single layer designed with a thicknessof ¼ of a wavelength of sound and having an acoustical impedance equalto the square root of the product of the acoustic impedances of the lensand the fluid. Alternately, the surface treatment may comprise acomposite layer comprised of multiple thicknesses of films whichgradually shift the impedance from that of the fluid to that of thelens. In an alternate embodiment, the surface treatment is a surfacefinish that has a peak to valley distance and peak to peak distance ofless than one wavelength. The surface finish is a pattern of grooves.The grooves are created with a lathe to construct concentric circles ofV shape cuts. Multiple radial cuts create peaks along the surface of thelens. Those skilled in the art will recognize that other methods ofcreating peaks and valleys are within the scope of the invention andother manufacturing techniques may be used such as molding, injectionmolding, laser machining, and chemical processing. Alternately, thesurface finish may be a random dimensional distribution of peaks.Alternately, the plurality of ultrasonic elements include one or moresurfaces of diffractive ultrasonics. The diffractive surfaces aregrooves with spatial relationships to effect a change in the peak of theultrasonic staves.

In one embodiment of the invention, the ultrasonic transducer generatessound energy with about 300 micron wavelength.

Refer now to Table A which shows a listing of a CODE V run. CODE V is anoptical design programing from Optical Research Associates, Inc. ofPasadena Calif. The ultrasound system of the invention has been modeledusing the CODE V design package. Each surface of the system is modeledusing a number of parameters. The model takes into account the radius ofthe surface relative to a point on the ultrasonic axis. The ultrasonicsurface is assumed to be spherical unless otherwise specified. Thematerial making up the surface is also specified.

TABLE A CODE V > res budibox File BUDIBOX.LEN (24) has been restoredwith tolerances and sensitivity coefficients CODE V > lis RDY THI RMDGLA CCY THC CLG > OBJ: INFINITY 150.000098 100 RED 1: 646.56671 3.100000‘TPX’ 100 100 2: 830.82936 12.400000 AIR 100 100 3: −79.35737 3.720000‘styrene’ 21 100 4: −162.88524 89.020775 34 0 ASP : K : 0.000000 KC :  100 IC :   YES CUF : 0.000000 CCF :    100 A : −.197598E−05 B :0.157598E−10 C : −.201574E−12 D: 0.000000E+00 AC :    80 BC :    81 CC :   82 DC: 100 STO : INFINITY 0.000000 100 COL 6 : 54.76050 7.440000‘styrene’ 67 COL ASP : K :    0.000000 KC :     100 IC :    YES CUF :   0.000000 CCF :   100 A : −.433031E−05 B : 0.594032E−09 C :0.157306E−12 D :-.125397E−15 AC :    90 BC :     91 CC :    92 DC: 93 7:   89.89027    16.6856285 ‘FC-40’ 0 0 ASP : K :   0.000000 KC :     100 IC :     YES CUF :    0.000000 CCF :    100 A : −.679678E−06 B: 0.473364E−11 C : 0.146454E−13 D :−.179238E−17 AC :     0 BC :     0 CC:    0 DC: 0 8 : −578.81495  2.480000 ‘styrene’ 13 100 9 : −578.81495 0.000000 ‘stuff’ 100 100 10 : INFINITY 69.396383 100 PIM IMG : INFINITY 0.046822 100 0 SPECIFICATION DATA: EPD 76.86552 DIM   MM WL 300000.00REF    1 WTW    1 XOB 0.00000 0.00000 0.00000 0.00000 YOB 0.0000020.00000 40.00000 56.60000 VUX 0.00000 0.00699 0.02938 0.05924 VLX0.00000 0.00699 0.02938 0.05924 VUY 0.00000 0.08451 0.20589 0.59048 VLY0.00000 −0.05673 −0.09289 −0.00216 APERTURE DATA/EDGE DEFINITIONS CA CIRS7 41.000000 CIR S2 EDG 67.889504 PRIVATE CATALOG PWL 300000.00 ‘FC72’2.910000 ‘stuff’ 1.100000 ‘1dpeth’ 0.764000 ‘bakelite’ 0.937000 ‘rtv511’1.340000 ‘TPX’ 0.671000 ‘styrene’ 0.621000 ‘FC-40’ 2.345000 REFRACTIVEINDICES GLASS CODE 300000.00 ‘TPX’ 0.671000 ‘styrene’ 0.621000 ‘FC-40’2.345000 ‘stuff’ 1.100000 SOLVES RED 0.320000 PIM No pickups defined insystem INFINITE CONJUGATES EFL 71.6086 BFL 46.4816 FFL 73.7769 FNO0.9316 AT USED CONJUGATES RED 0.3200 FNO 1.2300 OBJ DIS 150.0001 TT354.2897 IMG DIS 69.4432 OAL 134.8464 PARAXIAL IMAGE HT 18.1120 THI69.3964 ANG 10.4895 ENTRANCE PUPIL DIA 76.8655 THI 142.9414 EXIT PUPILDIA 79.5818 THI −27.6575

Where:

EPC is the entrance pupil diameter,

WL is the wavelength,

REF is the reference surface,

WTW is the wavelength weight for multiple wavelengths,

XOB, YOB are the object height,

VUX, LX, VUY, VLY are vignetting factors,

CIR defines a circular aperture,

RED is the reduction ratio of the system,

EFL is the effective focal length,

BFL is the back focal length,

FFL is the front focal length,

FNO is the f number,

TT is the total track,

OAL is the object dispersion angle, and

ANG is the angle of the image to the center ray.

All indexes of refraction are computed relative to air to accomplish theultrasonic simulation.

In operation, the lens system 2210 focuses energy reflected from anexample object 2222 onto the image of an object 2224. The image of theobject is detected by an ultrasonic transducer/receiver.

The images obtained by the lens system are enhanced by the interactionof the two main elements 2216 and 2218. Both elements work together tocompensate for various aberrations, including spherical aberration,coma, astigmatism, and distortion. The system is designed to work atabout 300 microns of ultrasonic signal and with a quasi acousticalsource.

The ultrasonic camera may be made less costly and easier to manufacturesince the ultrasonic camera requires relatively few parts. Theultrasonic camera is also more efficient because fewer elements absorbless energy. Fewer elements also reduce the amount of reflection, alsoimproving the performance of the system.

Refer now to FIG. 24 which shows an alternate embodiment of theultrasonic lens 2211 of the invention. The ultrasonic lens 2211 isidentical to ultrasonic lens 9210 shown in FIG. 23, except that theentrance window 2215 is shaped to better conform to certain anatomicalfeatures of the human body for mammography. FIG. 23 also illustrates theflexibility of the invention to be applied to differing ultrasonicenvironments. The entrance window 2215 can be further shaped to fitother anatomical features for both human and animal subjects.

The invention may be applied to underwater imaging environments such asmine detection. The invention may also be applied in petroleumenvironments for imaging in wells and drill holes.

Refer now to FIG. 25 which shows one embodiment of the stretchedmembrane interface of the invention. The stretched membrane interface2318 is stretched over mount 2402 and held taut to provide an air/waterbarrier. The membrane 2318 is coupled to the ultrasonic array 2312 witha film 2404 of coupling fluid such as oil. The ultrasonic array 2312 ispositioned on the air side 2408 of the stretched membrane interface2318. The water filled side 2406 faces the ultrasonic lens system 2324,shown in detail in FIG. 23. The use of water and the oil film provides aultrasonically advantageous path for transmission of ultrasonic energy.

The membrane 2410 of the stretched membrane interface 2318 may beconstructed from polymethylpentene also known as TPX, polyethylene orpolyester. The membrane 2410 serves to hold the water on one side of themembrane 2410 and allows the ultrasonic array 2312 to be mounted on theair side. Those skilled in the art will appreciate that other suitablematerials may be used. The material and thickness of the membrane may beselected for optimum sound transmission from the water 2406 into theultrasonic array 2312. In an example embodiment of the invention, themembrane 2410 is made as thin as possible, i.e., less than {fraction(1/10)} of a sound wavelength, in one example, about 30 microns.

In an alternate embodiment of the invention, the membrane 2410 isdesigned to make the acoustical impedance of the membrane 2410 equal tothat of water. Acoustical impedance equals the velocity of sound timesthe density of the conduction medium. TPX is a good material toconstruct the membrane 2410 from because TPX has an impedance very closeto water.

In another alternate embodiment of the invention, the membrane 2410 isdesigned with a thickness of ¼ of a wavelength of sound and designed tomake the membrane's acoustical impedance equal to thesqrt(Z_(water)×Z_(array)). Where Z_(water is) 1.5 Mrayls and Z_(array)may be typically 20 Mrayls. This approach is analogous to the use of anantireflection coating on an optical lens.

The shape of the mount 2402 may be circular ring or similar shape thatcreates a membrane that is flat and taut then the membrane 2410 isstretched across it. The circular ring creates a flat, taut, drumheadshape.

The stretched membrane interface 23318 is fixed to the mount 2402 with aretaining ring 2412. The retaining ring 2412 has a first ring 2414 thatencircles the mount 2402 and is threaded on an inside diameter to mateto threads on the mount 2402. A second ring 2418 also encircling themount 2402 clamps the stretched membrane interface 2318 to the firstring 2414. The second ring 2418 is held to the first ring 2414 by anumber of bolts placed around the circumference of the second ring 248as exemplified by bolts 2416A and 2416B.

The oil film 2404 is used to couple the ultrasonic array 2312 to themembrane 2410. Ultrasound at certain frequencies does not transmiteffectively through an air film, so that the coupling material isessential for the operation of the invention. The oil film should be asthin as possible, preferably less than {fraction (1/100)} of thewavelength of the sound. The membrane 2318 forms an acoustic interfacethat conducts collected ultrasonic energy into the ultrasonic conductionmedium 2406 and provides mechanical isolation of the transductioncircuitry. The flat surface of the membrane 2318 provides a mechanicalinterface assuring, six dimensional (X, Y, Z, roll, pitch, yaw)alignment of the ultrasonic lens 2210 in relation to the transductioncircuitry, ultrasonic array 2312. The opening through the mount 2402provides unimpeded acoustical contact of the transduction means to themembrane.

The membrane provides for separating fluid in the collection apparatusfrom the transduction electrical circuitry, ultrasonic array 2312. Themembrane further provides for ease of separation of the collectionapparatus from the transduction apparatus, ultrasonic array 2312 and forimpedance matching of the collection apparatus to the transductionapparatus. The membrane also provides transverse acoustical decouplingof the membrane from the transduction apparatus. Thus, the membranereduces crosstalk between transducers.

In one embodiment, the oil film 2404 between the membrane 2318 and thetransduction apparatus, ultrasonic array 2312 is less than 10% of awavelength. In one embodiment, the oil film 2404 is a gel film.

Refer now to FIG. 26 which shows one alternate of the ultrasonictransmitter of the invention. The ultrasonic transmitter 2316, in oneembodiment, operates as a quasi incoherent acoustical source. A quasiincoherent acoustical source attempts to behave like a completelyincoherent acoustical source, much like a white incandescent light bulbapproximates an incoherent optical source. The ultrasonic transmitter2316 provides a source of ultrasound that is both temporally incoherentas well as a spatially incoherent.

The benefit of an incoherent sound source for insonification of theobject 2304 can be understood with an analogy to optical coherentimaging. When an object is insonified by a coherent optical source, suchas a laser, the resulting picture or image appears speckled. Thisspeckling makes the object difficult to view. When an object isinsonified by a white light source, the images are clear and sharp.Similarly, with ultrasonic imaging a coherent source produces ananalogous speckled ultrasonic image.

The invention achieves the quasi incoherent acoustical source byproviding an array of ultrasonic transmitters with special designfeatures. FIG. 26 shows the array 2600 having rows 2604 and columns 2608of transmitters. Other configurations of the transmitters are possible,such as a linear configuration or a radial configuration. Theseconfigurations may comprise a rectangular pattern, a circular pattern, areticulated pattern, a diagonal pattern, a grid pattern, a randompattern, a triangular pattern, a cross pattern or an oval pattern. Eachtransmitter is a member of a group of transmitters randomly distributedabout the array. Each member of the group shares the property in thatthey have been tuned to the same resonant frequency. There are multiplegroups, each group having a unique resonant frequency.

The resonant frequency may be changed by a number of approachesincluding attaching a predetermined mass to the transmitter. The extramass attached to the ultrasonic transmitter changes its resonancefrequency.

In one example embodiment, the array 2600 is broken into 128 groupswherein each group contains 128 transmitters distributed randomly aroundthe array. Each group has a unique weighted mass made from gold,platinum or any other stable, easy to deposit or suitable metal attachedto the transmitter to change its resonance frequency. This allows thetransmitter to respond differently to an identical stimulus, providing,a quasi incoherence in the response. Each transmitter is designed totransmit in a range from approximately low ultrasound frequencies, suchas 100 kHz, up to high ultrasound frequencies, such as 15 MHz.

In another example, the array contains 16 thousand transmitters. Eachgroup in the array contains 100 transmitters, providing for 160 groups.

Each group is driven by a pulse driver such as an RF powered amplifier,shown for group 1 as amp 2618, for group 2 as amp 2620, for group 3 asamp 2622, and for group N as amp 2624. Each transmitter group is drivencompletely independently. The array 2600 further provides a temporalincoherence by varying the drive signal to each group with group drivercontrollers 2630, 2632, 2634 and 2638. Each group driver controller isinterfaced to the ultrasonic camera controller 2334 by programmableinterface 2640 that can change the drive signals to each group.

There are two types of drive signals that are contemplated by theinvention. The first signal comprises a short tuned burst of apredetermined number of cycles of sine waves. A short burst of a sinewave is also known as a gated sine. In one example embodiment, groupdriver controller 2630 is programmed to generate a number of cycles of asine wave, such as from two to three to up to five cycles. The frequencyof the wave can vary from a nominal amount of one MHz, down to half aMHz, and up to two MHz.

The second type of drive signal is an impulse signal. When using theimpulse, the group is driven by the impulse to have a random amount ofwaiting time varying from no wait to more than the period of theoperating frequency of the array 2600. In an example embodiment, groupdriver 2638 stimulates driver 2624 with an impulse and waits a randomamount of time before stimulating driver 2624 again. The overall arraytiming is controlled by programmable controller 2640 that is interfacedand controlled with the ultrasonic camera controller 2334. After therandom wait time, another random group is stimulated with the sameimpulse. Both of these methods provide spatially and temporallyincoherence insonification of the object 2304.

Other types of drive signals are contemplated by the invention, such asdifferent wave shapes and stimulus duration, as well as different typesof impulse, and impulse like drive signals.

FIG. 27 shows an acoustical imaging system 2700 having an ultrasoundcamera 2710 connected to a signal processor 2720 with four acousticaltransmitters 2712, 2714, 2716 and 2718. The ultrasound camera 2710 maybe the ultrasonic camera shown in FIG. 22. Each transmitter has aprincipal axis of ultrasonic insonification. The quasi incoherentacoustical source can be approximated by using a multiple number ofcoherent acoustical sources that are varied in time and thatacoustically illuminate the object at different principal angles ofinsonification. The ultrasonic sensor 2700 operates by transmitting acoherent beam from transmitter 2712 and taking a picture with the imager2710. A second picture of the same scene is then taken with the imager2710 insonified by a second source 2714. This process is repeated forsource 2716 and 2718. The resulting four pictures are then addedtogether to present a much smoother averaged image. The resulting imageapproximates one that would result from a system using a quasiincoherent acoustical source. The plurality of ultrasonic transmittersare driven sequentially to produce separate images of the object. Thesignal processor 2720 converts the sequential images to produce an imageof the object of high quality by averaging two or more of the sequentialimages. In yet another alternate embodiment, a single ultrasonictransmitter may be sequentially moved to a new ankle of insonification.Alternatively, the multiple transmitter array may be electronicallysteered to a new angle of insonification. The electronic steering may beaccomplished using conventional phase array techniques that alter thephase and timing of each element.

In one embodiment of the multiple transmitter array, groups oftransmitters are constructed with different mechanical characteristicsand are driven with the same signal. The different mechanicalcharacteristics of the transmitter groups may be accomplished bydesigning the transmitter groups to have different resonancefrequencies. Alternatively, different mechanical characteristics areachieved through different vertical spacings. The drive signal of themultiple transmitter array may comprise one or more electrical pulses.The electrical pulse may comprise an electrical sine wave burst, wherefrequency of the sine wave burst corresponds to the resonance frequencyof each group of transmitters. Alternatively, the drive signal maycomprise an electrical sine wave burst of a single frequency.

FIG. 28 shows an acoustical transducer hybrid array 2801 having an array2802 of transducer elements 2803. Each transducer element 2803 uses abump interconnection 2804 to connect to the silicon readout ortransmit/readout integrated circuit 2805. The silicon readout ortransmit/readout integrated circuit 2805 includes an electronic unitcell 2806 having a preamplifier connected to the bump interconnection2804 as described above. The bump interconnection 2804 is connected toan individually isolated driving layer 2812. The bump interconnection2804 has a predetermined size that is small relative to the size of theultrasonic transducer. The individually isolated driving layer 2812electrically connects the subelements and may be constructed of gold orother suitable conductor. Transducer 2803 is shown without theindividually, isolated driving layer 2812 for clarity. The individuallyisolated driving layer 2812 is shown connecting the four subelements oftransducer 2815. The silicon readout or transmit/readout integratedcircuit 2804 also comprises signal processing and storage elements asdescribed above. A common electrode 2814 electrically connects alltransducer elements. Each transducer element 2803 is constructed ofsubelements 2807, 2808, 2809 and 2810. Each subelement may also becalled a post. Each transducer element may be constructed from PZT-5Halso known as lead zirconate titanate. Other suitable materials may alsobe used. In one example, the size of the transducer may be 0.2millimeters by 0.2 millimeters. The space between the posts is filledwith a filler such as epoxy DER332 from Dow Chemical Inc. In oneembodiment, the epoxy 2811 may be a soft epoxy. The posts may bepositioned at the corners of the transducer or anywhere in between. Inan alternate preferred embodiment, the transducer element 2803 may havenine posts. The posts may also be round as well as square. The objectiveis to create posts with a high aspect ratio of height to width. Thetransducer element 2803 is said to have its volume fraction reduced bythe division into four subelements. As shown in FIG. 29, the lower thevolume fraction, the higher the ultrasonic sensitivity and the lower thecapacitance of the transducer. The volume fraction is defined as thevolume of the subelements divided by the volume of the subelements andthe filler epoxy. In one example, the volume fraction may range from 10%to 50%. Conventional composite arrays are constructed with volumefractions of between 70% to 80%. The subelements may be constructed bysawing grooves in the ceramic, injection molding, chemical etching,laser ablation, and ion milling or other suitable method.

Conventional ultrasonic systems use micro-coaxial cable to connect thearray to the front end electronics. Although micro-coax technology hasimproved dramatically in the past decade, interconnecting 16,384 arrayelements with separate wires remains a formidable challenge. In additionto this practical fabrication issue, the capacitance of a long coaxialcable (typically 40 pF/m) is much larger than that of a typical 2D arrayelement (<1 pF). This creates a voltage divider that severely reducesthe signal-to-noise ratio of the channel. The direct connection methodusing solder bumps 2804 reduces the interconnect length to less than 0.1mm, reducing interconnection capacitance to a level where it is nolonger a dominant factor in the channel signal-to-noise ratio.

The interconnection method is shown in FIG. 28. Solder bumps 2804 aredeposited on both the array 2802 and the silicon integrated circuit2805. During hybridization, the bumps 2804 are optically aligned andbrought into contact to make an electrical connection. The contact areaof the bumps on the array is approximately 20×20 microns, which providesadequate mechanical integrity, good electrical contact and has a minimalbut not negligible, effect on the acoustics of an air-backed transducerdesign.

With this interconnection method, the input electronics has acapacitance of less than 100 fF. This provides a unique opportunity tooptimize the composite piezoelectric material that is not available toconventional ultrasound systems. FIG. 29 plots the piezoelectriccoupling co-efficient 2901, capacitance 2902 and sensitivity 2903 at aconstant resonance frequency as a function of piezoceramic volumefraction as described by W. A. Smith and B. A. Auld in “Modeling 1-3Composite Piezoelectrics: Thickness-Mode Oscillations,” IEEE Trans.Ultrasonics Ferroelectrics and Frequency Control, UFFC-38: 40-47 (1991).By reducing the volume fraction of ceramic, sensitivity can be increasedat the expense of lower capacitance while maintaining high coupling.This transducer hybrid assembly attains high efficiency by exploitingthis phenomenon due to its particular structure.

The array may be configured to provide a quasi acoustical source asdescribed above. The additional metal masses may be placed on top of theindividually isolated driving layer 2812. Alternately an increase inmass may be accomplished by increasing the thickness of the individuallyisolated driving layer 2812. Alternately, the additional mass may beadded by including additional metal to the common electrode end of thetransducer 2814. In yet another embodiment, the lengths of thetransducers may be varied to accomplish the variations in mass.Variations in length may be taken up by additional epoxy or the commonelectrode layer 2814.

The ultrasonic array 2312 may be operated in a send only mode or asend/receive mode utilizing the array 2801 of FIG. 28. In thesend/receive mode the ultrasonic array 2312 provides the ultrasonicinsonification. The array 2801 of FIG. 28 may be used in the transmitter2316 of FIG. 22 and transmitters of FIG. 27 and as the array 2602 inFIG. 26. The invention provides a means for transducing the conductedelectronic energy into electrical signals having a low volume fractionpiezoelectric composite material in combination with a low capacitanceelectrical bump bond interconnection to a low stray capacitancepreamplifier integrated circuit.

The invention has been described herein in considerable detail in orderto comply with the Patent Statutes and to provide those skilled in theart with the information needed to apply the novel principles and toconstruct and use such specialized components as are required. However,it is to be understood that the invention can be carried out byspecifically different equipment and devices, and that variousmodifications, both as to the equipment details and operatingprocedures, can be accomplished without departing from the scope of theinvention itself.

What is claimed is:
 1. An ultrasonic lens system comprising: (a) an lens housing having a mount; and (b) a plurality of ultrasonic elements attached to the mount wherein the plurality of ultrasonic elements cooperate to transmit ultrasonic radiation at high efficiency with low aberration.
 2. The apparatus of claim 1 wherein high efficiency is achieved by a surface treatment that adjusts the acoustic impedance of the ultrasonic elements to a surrounding fluid.
 3. The apparatus of claim 2 wherein the surface treatment is a single layer designed with a thickness of ¼ of a wavelength of sound and with an acoustical impedance equal to the square root of the product of the acoustic impedances of the ultrasonic elements and the surrounding fluid.
 4. The apparatus of claim 2 wherein the surface treatment is a composite layer comprised of multiple thicknesses of films that gradually shift an impedance from that of the surrounding fluid to that of the ultrasonic elements.
 5. The apparatus of claim 2 wherein the surface treatment is a surface finish which has a peak to valley distance and peak to peak distance of less than one wavelength.
 6. The apparatus of claim 5 wherein the surface finish is a pattern of grooves.
 7. The apparatus of claim 5 wherein the surface finish is a random dimensional distribution of peaks.
 8. The apparatus of claim 1 wherein the plurality of ultrasonic elements includes a surface of diffractive ultrasonics.
 9. The apparatus of claim 8 wherein the surface of diffractive ultrasonics comprise grooves with spatial relationships to effect a change in the path of the ultrasonic waves.
 10. The apparatus of claim 1 wherein the ultrasonic radiation has a wavelength of approximately 300 microns.
 11. The ultrasonic lens system of claim 1 wherein the plurality of ultrasonic elements further comprise a first ultrasonic lens mounted to the mount having a first spherical surface and a first aspherical surface and a second ultrasonic lens mounted to the mount having a second aspherical surface, a third aspherical surface and a second spherical surface and a third spherical surface.
 12. The apparatus of claim 11 wherein the first spherical surface has a first surface radius of about −79.35737 mm.
 13. The apparatus of claim 11 wherein the first aspherical surface has a second surface radius of about −162.88524 mm and the first aspherical surface is defined by the equation: $Z = {\frac{{cx}^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {Ax}^{4} + {Bx}^{6} + {Cx}^{8} + {Dx}^{10}}$

where c=1/radius, radius=54.76050 mm, K is the conic constant which is zero 0.0 in this case, A=−0.433031E-05, B=0.594032E-9, C=0.157306E-12, and D=−125397E-15.
 14. The apparatus of claim 11 wherein the second aspherical surface has a third surface radius of about 54.76050 mm and the second aspherical surface is defined by the equation: $Z = {\frac{c\quad x^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {A\quad x^{4}} + {B\quad x^{6}} + {C\quad x^{8}} + {D\quad x^{10}}}$

where c=1/radius, radius=89.89027 mm, K is the conic constant which is zero 0.0 in this case, A=−0.679678E-06, B=0.463364E-11, C=0.146454E-13, and D=−0.17928E-17.
 15. The apparatus of claim 11 wherein the third aspherical surface has a fourth surface radius of about 89.89027 mm and the third aspherical surface is defined by the equation: $Z = {\frac{c\quad x^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {A\quad x^{4}} + {B\quad x^{6}} + {C\quad x^{8}} + {D\quad x^{10}}}$

where c=1/radius, radius=89.89027 mm, K is the conic constant which is zero 0.0 in this case, A=−0.679678E-06, B=0.473364E-11, C=0.146454E-13, and D=0.179238E-17.
 16. The apparatus of claim 11 wherein the second spherical surface has a fifth surface radius of about −578.81495 mm.
 17. The apparatus of claim 11 Wherein the third spherical surface has a sixth surface radius of about −578.81495 mm.
 18. The apparatus of claim 11 wherein the first ultrasonic lens is made from polystyrene.
 19. The apparatus of claim 11 wherein the second ultrasonic lens is a liquid filled polystyrene lens.
 20. The apparatus of claim 19 wherein a liquid in the liquid filled polystyrene lens is FC40.
 21. The apparatus of claim 1 wherein the lens housing is filled with water.
 22. An ultrasonic lens system comprising: (a) a first ultrasonic lens made from polystyrene having a first radius of curvature of about −79.35737 mm, and a second radius of curvature of about −162.88524 mm, with an aspherical surface defined by the equation: $Z = {\frac{c\quad x^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {A\quad x^{4}} + {B\quad x^{6}} + {C\quad x^{8}} + {D\quad x^{10}}}$

where c=1/radius, radius=54.76050 mm, K is the conic constant which is zero 0.0 in this case, A=−0.433031E-05, B=0.594032E-9, C=0.157306E-12, and D=−125397E-15, and a first thickness through the ultrasonic center of 3.72 mm; and (b) a second fluid filed ultrasonic lens made from polystyrene having a third radius of curvature of about 54.76050 mm with a second aspherical surface defined by the equation: $Z = {\frac{c\quad x^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {A\quad x^{4}} + {B\quad x^{6}} + {C\quad x^{8}} + {D\quad x^{10}}}$

where c=1/radius, radius=89.89027 mm, K is the conic constant which is zero 0.0 in this case, A=−0.679678E-06, B=0.463364E-11, C=0.146454E-13, and D=−0.179238E-17, a third aspherical surface with a fourth radius of curvature of 89.89027 mm having a fourth aspherical surface defined by the equation: $Z = {\frac{c\quad x^{2}}{\left( {1 + \sqrt{\left( {1 - {\left( {1 + k} \right)c^{2}x^{2}}} \right)}} \right)} + {A\quad x^{4}} + {B\quad x^{6}} + {C\quad x^{8}} + {D\quad x^{10}}}$

where c=1/radius, radius=89.89027 mm, K is the conic constant which is zero 0.0 in this case, A='0.679678E-06, B=0.473364E-11, C=0.146454E-13, and D=0.179238E-17, and a second thickness through the ultrasonic center of 7.44 mm, a fifth radius of curvature of about −578.81495 mm located about 89.028 mm from the fourth radius, and a sixth radius of curvature of about −578.81495 mm with a third thickness through the ultrasonic center of 2.48 mm. 